[Solved] How do I parse in go the returned JWT token from google OAuth 2.0?

Quick Fix: Import the "github.com/golang-jwt/jwt/v5" library for parsing JWT tokens. Use the "github.com/MicahParks/keyfunc/v2" library to retrieve and cache Google’s public keys for token validation. Implement a caching mechanism to update the public keys periodically based on the Cache-Control header in the response. Utilize the "jwt.Parse" function to parse the JWT token and verify its signature using the public keys obtained from the keyfunc library.

The Solutions:

Solution 1: Parse JWT using Google’s Public Keys

Validate the Google OAuth 2.0 JWT using Google’s public keys rather than the secret you created. Here’s how to do it:

Fetch the JSON Web Key Set (JWKS) from Google’s public keys URL: https://www.googleapis.com/oauth2/v3/certs.
Create a new keyfunc object from the fetched JWKS using the NewJSON function from the keyfunc library.
Use the Parse function from the jwt library to parse the JWT from Google using the Keyfunc as the key retrieval function.
Check if the JWT is valid and access the claims if it is.

Example code for parsing the JWT using Google’s public keys:

func parseJWT(tokenString string) {
    jwksJSON := json.RawMessage(getGoogleCerts())
    jwks, _ := keyfunc.NewJSON(jwksJSON)

    token, _ := jwt.Parse(tokenString, jwks.Keyfunc)
    if token.Valid {
        claims := token.Claims.(jwt.MapClaims)
        fmt.Println(claims["email"], claims)
    } else {
        fmt.Println("Invalid JWT")
    }
}

Remember to cache the JWKS JSON for a period of time as specified in the Cache-Control header of the response from Google’s public keys URL.

Q&A

How do I parse the returned JWT token from google OAuth 2.0?

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Use Google’s public keys at https://www.googleapis.com/oauth2/v3/certs to verify the token’s signature.

How do I cache the public keys?

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Hit the URL and cache the JSON response for a period defined in the Cache-Control header.

Can you provide code example?

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Check out the main.go file at https://github.com/MicahParks/keyfunc/blob/master/examples/json/main.go

Video Explanation:

The following video, titled "How to fix Unexpected Token in JSON error (for web developers ...", provides additional insights and in-depth exploration related to the topics discussed in this post.